Description:

Objective:

Particular microbial populations may be selectively
enhanced by the introduction of specific organic nutrients into the rhizosphere
environment.
The objectives of this research project are to assess: (1) the impact of exogenous
applications of the organic nutrient myo-inositol on rhizosphere bacterial
populations; and (2) the potential for creating biased rhizosphere systems
and evaluating their usefulness in specifically stimulating target populations
of rhizosphere bacteria.

Approach:

The rhizopine synthesis (mos) genes from Sinorhizobium
meliloti L5-30 were used to generate rhizopine-producing transgenic plants.
Rhizopines
did not accumulate in transformed plant tissues, and molecular analyses indicated
that not all of the cloned mos genes were properly expressed. An analysis of
the cloned mos genes suggested that they were not sufficient for rhizopine
accumulation in nodules. More information regarding the nature of rhizopine
synthesis is required before a biased rhizosphere system based on rhizopine-synthesizing
plants can be created. The abundance and source of rhizopine catabolic activity
in the soil and rhizosphere environment also were investigated. The number
of culturable bacteria capable of utilizing these compounds for growth was
1 to 10 percent of the number growing on complex media. A diverse set of novel
rhizopine-catabolizing bacteria was isolated and characterized. Different bacteria
that can catabolize the proposed nutritional mediators are present in the environment
and may compete for these organic nutrients in situ. The impact of myo-inositol
amendment on soil and rhizosphere bacterial populations was examined in growth
chamber and field experiments. The application of the nutrient resulted in
increases in the numbers of culturable bacteria. Amplified rDNA restriction
analysis (ARDRA) and fluorescence-tagged ARDRA indicated that the abundance
and composition of the bacterial communities changed in response to the amendment.
Increases in the abundance and activity of S. meliloti were observed. These
results indicate that nutrient amendments can be used to promote the growth
and activities of targeted bacterial populations in the rhizosphere.

The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.